1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, particularly to an electrophotographic photosensitive member containing a trisazo pigment having a specific molecular structure in the photosensitive layer.
2. Related Background Art
In the prior art, as the electrophotographic photosensitive member using an inorganic photoconductive substance, those by use of selenium, cadmium sulfide, zinc oxide, etc. have been widely known.
On the other hand, as the electrophotographic photosensitive member using an organic photoconductive substance, those by use of a photoconductive polymer as represented by poly-N-vinylcarbazole or a low molecular weight organic photoconductive substance such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, and further combinations of such organic photoconductive substance with various dyes and pigments have been known.
The electrophotographic photosensitive member using an organic photoconductive substance has advantages that it has good film formig property, can be produced by coating, is high in productivity and capable of providing inexpensive photosensitive members. Also, it has the advantage that color sensitivity can be freely controlled by selection of the dye or pigment to be used, and therefore broad investigations have been done up to date about such photosensitive members. Particularly recently, by development of a function separation type photosensitive member having a charge generation layer of an organic photoconductive pigment and a charge transport layer comprising a photoconductive polymer or a low molecular weight photoconductive substance as described above laminated, sensitivity and durability which have been the drawbacks of the organic electrophotographic photosensitive member of the prior art have been remarkably improved to enable practical application thereof possible.
Further, in recent years, with propagation of laser beam printers, it has been abundantly done to develop an electrophotographic photosensitive member having sensitivity to the long wavelength region around 800 nm, and further an electrophotographic photosensitive member capable of obtaining uniform sensitivity over 760 nm to 800 nm in view of the oscillating width in the oscillation wavelength region of the laser, and as the organic photoconductive azo pigment to be used in such photosensitive member, for example, biphenylamine type disazo pigments disclosed in Japanese Laid-open Patent Publication No. 61-43662 and triphenylamine type trisazo pigments disclosed in Japanese Laid-open Patent Publication No. 53-132347. etc. have been known. The electrophotographic photosensitive members using these azo pigments, while having excellent sensitivity, are on the other hand not sufficient in charging ability, dark decay, potential stability during repeated uses.
Further, the benzanthrone type disazo pigments disclosed in Japanese Laid-open Patent Publications Nos. 59-31962, 61-219048 and 62-127845 have excellent sensitivity and potential stability, but were still insufficient in aspect of flatness of sensitivity in the laser oscillation wavelength region.